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1 TO: UNCLASSIFIED AD NUMBER AD LIMITATION CHANGES Approved for public release; distribution is unlimited. FROM: Distribution authorized to U.S. Gov't. agencies and their contractors; Administrative/Operational Use; 31 MAR Other requests shall be referred to Air Force Technical Applications Center, Washington, DC. AFTAC ltr 28 Feb 1972 AUTHORITY THIS PAGE IS UNCLASSIFIED

2 177 O^ THE (pp-p) TIME DIFFERENCE 31 March 1967 Prepared For AIR FORCE TECHNICAL APPLICATIONS CHSJTER Washington, D. C. By J, R. Woolson TELEDYNE, UK). Under Project VELA tinifom D D C 1^ APR 6 ^ B Sponsored By ADVANCED RESEARCH PROJECTS AGENCY Nuclear Test Detection Office ARPA Order No. 624

3 I THE (pp-p) TIME DIFFERENCE SEISMIC DATA LABORATORY REPORT NOo 177 AFTAC Project: Project Title: ARPA Order No.: ARPA Program Code No.: VELA T/6702 Seismic Data Laboratory Nc,me of Contractor: TELEDYNE, INC Contract No.: Date of Contract: Amount of Contract: Contract Expiration Date; Project Manager: F C March 1967 $ 1,735,617 2 March 1968 William C. Dean (703) P. O. Box 334, Alexandria, Virginia AVAILABILITY This document is subject to special export controls and each transmittal to foreign governments or foreign national may be made only with prior approval of Chief, AFTAC.

4 > This research was supported by the Advanced Research Projects Agency, Nuclear Test Detection Office, under Project VELA-UNIFOPM and accomplished under the technical direction of the Air Force Technical Applications Center under Contract F C Neither the Advanced Research Projects Agency nor the Air Force Technical Applications Center will be responsible for information contained herein which may have been supplied by other organizations or contractors, and this document is subject to later revision as may be necessary.

5 TABLE OF CONTENTS ABSTRACT THE (pp-p) TIME DIFFERENCE STATISTICAL ANALYSIS OF (pp-p) TIME DIFFERENCE CONCLUSIONS FIGURES 1. (pp-p) - Times 2. Examples of Seismograms Used TABLES 1. Kurile Earthquake - 18 May North Coast Chile Earthquake - 30 July Peru Earthquake - 10 May Chile-Bolivia Earthquake - 16 April 1965 Page No 1 2 4

6 ABSTRACT An inv e8 ti g atlon to cosine FEMOSE «1th velocity filtering over e three component array In ordev to enhance depth phaaes e.- perlencea conslderahle difficulty In allonvng P and pp phaaea elultaneously. To explain thla difficulty, B ela.o g ra mb fro. ur earthguakee were analyzed at the 9 altea In the TPO Extended ray. The depth phaae (pp) 1. well-defined on theae..l-^r.».. a eatahllahed that the ti». difference ( pp-p> at the 9 atat.ona of the array differ* by as uch aa 0.5 aeconda for the aaue earth- ^ak,. It la concluded that each phase P, PP. and In one caae Z. hae Ita own travel ttae anfalle, for the TPO Extended Array. «la further concluded that EEMODE ahould he applied to the three component aela^grama, rather than to the aum of the horizontal and vertical componenta of the array.

7 1. THE (PP-P) TIME DIFFERENCE There is a difference in the travel-time anomaly for P and pp at the TFO Extended Array. This difference is sufficient in some cases to result in near cancellation of pp if the seismograms are summed by aligning on P. On most seismograms it is not possible to determine the time of pp with sufficient accuracy to justify the above statement. If, however, the examples are limited to seismograms with well-defined pp, then the scatter of the time difference (pp-p) can be demonstrated. Four groups of seismograms were selected from the vertical seismograms recorded at the TFO Extended Array for the following earthquakes: Chile-Bolivia Earthquake - 16 April 1965 Peru Earthquake - 10 May 1965 N. Coast Chile Earthquake - 30 July 1965 Kurile is. Earthquake - 18 Aay 1965 The time difference (pp-p) observed" at the 9 stations of the TFO Extended Array for the above earthquakes were plotted on Figure 1 against A (surface distance). In each case the scatter of the points was about 0.5 seconds. The points were read by timing a well-defined peak or through, rather than attempting to read first motion. The parametric lines in Figure 1 were plotted from the Jeffreys- Shimshoni Tables (Jeffreys and Shimshoni 1964). They establish a norm against which the slope and scatter of the pp-p times may be measured. The parametric values of h/r for values other than 0.00, 0.01 and 0.02 were interpolated from the tables. As a result of using well-defined phases and selected earth- quakes the times for both P and pp are believed to be correct with 0.1 second. -1-

8 . I'l.. The Jeffreys-Bullen tables predict an increase in the time difference (pp-p) as a function of A (surface distance) and depth of focus measured by h/r, where h is hypocentral depth minus 33 km. and R is the earth*s radius. This increase is measured by the slope of the h/r plots of Figure 1. It varies from 0.1 second for the Kurile Earthquake to slightly more than 0.2 seconds for the Chile-Bolivia Earthquake across the range of surface distances measured by the TFO Extended Array. The spread of surface distances, observed by the TFO array, is commonly 3 to 4? varying with azimuth. Figure 2 consists of reduced copies of a representative seis- mogram from each of the four earthquakes used in this study. As noted earlier, well-defined phases were used to determine the time difference (pp-p). Tables 1 through 4 are the listings of the arrival times as determined from the 10 sees - 2 inches playbacks of the seismograms. Estimated reading accuracy is + 0.1: as based on reading the times one day, setting the values aside, and making an independent read- ing the following day. 2. STATISTICAL ANALYSIS OF (pp-p) TIME DIFFERENCES The visual evidence from the scatter of the plotted values of (pp-p) is clearly shown by Figure 1. In order to obtain a statis- tical measure of this scatter the following analysis was made. The relative smallness of the sample limits the conclusions to an indi- cation of the confidence limits. The mean and variances of the observed values of (pp-p) were computed using the standard formulas. n n *-> i-1 X i -2-.

9 and X n-. i=l (X, X)' The computed values are listed below. Kurile Eq. 18 May 1965 N. Coast Chile Eq. 30 July 1965 Peru Eq. 10 May 1965 Chile-Bolivia Eq. 16 P.pril 1965 (pp-p) The 95% confidence intervals of the variance were estimated from the following formula X (n-d S < a < &- X which resulted in the following data, for the four earthquakes enalyzed: Kurile Eq May > a 2 > N. Coast Chile Eq July > cr 2 > Peru Eq May > a 2 > Chile-BOlivia Eq April > a 2 > If the observed times for (pp-p) are all 0.1 second greater or less than the mean, the time differences of a pair becomes 0.2 seconds. The phase difference of a 1.0 sec period pulse is 1/5 x 360 or 72. This would be sufficient phase difference to produce some distortion: however, the signal would probably be -3-

10 Ilil III 111» recognizable. If this assumption is used as a basis for computation then > a 2 > This is the 95% confidence region, for the assumption each time is 0.1 sec greater or less than the mean is the above range. This difference (72 for 1 sec period) can be thought of as a threshold. If the time differences are greater, say 0.2, then the phase shift is 144 and summing produces near cancellation. This criteria of cancellation is not readily established, since the pulses to be summed contain a range of frequencies. It is probable that for reinforcement to occur, when the pulses are summed, requires a narrower range of variance than the range computed for the 0.1 second assumption. In each case the actual 95% confidence interval is greater than that computed for the 0.1 sec. assumption. 3. CONCLUSIONSt 1. Travel time anomalies for pp phases are different than those for P by as much as 0.5 seconds over the TFO Extended Array. 2. Because of the different travel time anomalies, signals aligned on P will misalign pp and vice versa. 3. Other compressional phases can be expected to require still different travel-time anomalies. In fact, pp phases from sources at different depths can be expected to require different travel time anomalies. 4. The application of REMODE operators to the summation traces from three component, short period seismic arrays will be considerably less than optimum unless different array alignments are imposed at different times during the earthquake signal. 5. The false signal rate for REMODE processors, due to chance waveform on matchings in vertical and horizontal traces, will be as high for array summation traces as for single seisroograms. -4- WMHI

11 ^L 6. Array summing of KEMODE outputs from three component sites will suffer the same phase misalignments as raw data. Thus, the recommended technique for REMODE processing of three component arrays is to REMODE each three component site as a unit and then display the results as a suite of seismograms, Array mixing of all verticals separately and all horizontals separately first is not a promising method of enhancing the sensitivity of REMODE for depth phases. -5-

12 Figur«1. (pp-p) - Tim««

13 - ^ Figur«1. (pp-p) - «*

14 «-_»^ ; i-jih in imii.a.. i i - -i 6346 j Chile Bolivia NL 5510 Peru Eq. ^'X^- ** ( t A/^V^ AA*- / W\A^"AAr' /s *'\r'" ty ' *» ^^/V,, -^Y% t N. Chile Eq. t * wo 5514 t^jwi^^if»^! ^jwi»«^) Mi Kurlie Eq. Figure 2. Examples of Seismogratns Used

15 Station & Seismoqram Number SG 5511 P EP (PP-P) 13.7 JR LG NL WO TPO SN HR GE Table 1. Kurile Earthquake - 18 May 1965 Station and Seismccrram Number SG 9023 JR 9027 NL 9022 LG 9024 WO 9026 TPO 9028 HR 9021 SN 9020 GE 9025 P , , , ^5 50, P (PP-P) Table 2. North Coast Chile Earthquake - 30 Juxy 1965 '9 -'"".

16 II Station and Seismoqram Number I P (PP-P) SG JR 6G NL LG WO TPO G HR SN GE Table 3. Peru Earthquake - 10 May 1965 Station Seismoqram and Number (PP-P), SG ( ) (31.6) JR ( ) (31.2) NL LG WO HR TPO SN GE Table 4. Chile-Bolivia Earthquake - 16 April 1965

17 Unclassified Security Classification DOCUMENT CONTROL DATA R&D (S.curUy cl...l«c.«o. ol «III«, body ol.>.t»cl gg Imtortn«mnol.Ucn m».t X «.«««d *««««'"'«" gg! " ««"""»"> a. KEFORT tlcuhitv C UAtdFIC* TION Unclassified TELEDYNE, INC. ab amour ALEXANDRIA, VIRGINIA I. ONIQINATINO ACTIUITY (Coipol»»» «uwi»«). neport TITLB THE (pp-p) TIME DIFFERENCE «QEtCRIPTIVE MOTf t (Tn>» ol npori ind IncHimln >lmf> Scientific Report S AUTHOWSJ (L»tl nam*. Drat naai«, Inlttml) Woolson, John R. «. RtPO RT DAT! 31 March 1967 «. CONTRACT OR «RANT NO. F C-1313 b. PROJCCTNO VELA T/6702 iß. "OTAL NO. or ** 10 RT'J SDL Report No. 177 «ARPA Order No. 624 A ARPA Program Code No 5810 tb OTHBR RKRORT H<K» (*«r»»»tnambti» mar» «# < Al«meit) This document is subject to special export controls and each transmittal to foreign governments or foreign nationals may be made only with prior "rrwyfll" 1 nf Chief. AFTAC It. trontoriho MILITARY ACTIVITY It. furrlemintarv NOTIt Advanced Research Projects Agency Nuclear Test Detection Office Waflhincrf-on D. C. is. ABSTRACT An investigation to combine REMODE with velocity filtering over a three component array in order to enhance depth phases experienced considerable difficulty in aligning P and pp phases simultaneously. To explain this difficulty, seismograms from four earthquakes were analyzed at the 9 sites in the TFO Extended Array. The depth phase (pp) is well-defined on these seismograms. It is established that the time difference (pp-p) at the 9 stations of the array differs by as much as 0.5 seconds for the same earthquake. It is concluded that each phase P, pp, and in one case sp, has its own travel time anomalies for the TFO Extended Array. It is further concluded that REMODE should be applied to the three component seismograms, rather than to the sura of the horizontal and vertical components of the array. DD ^ 1473 Unclassified Security Claaaificalion

18 ünrl absi.fi p/1... Security Clasgificatiwi KEY WORDS LINK A REMODE velocity filtering three component array depth phases! 1 " INSTRUCTIONS imposed by security daaalflcatlon, using standard statements uch : (X) "Qualified requesters may obtain copies of this report from DDC" (2) "Foreign snnouncement end dissemination of this report by DDC Is not authorized" (3) "U. 8. Government agencies may obtain cojl of thla report directly from DDC Other qualified DDC. users shall request through 1. ORIGINATING ACTIVITY: Enter the name and addre» of the contractor, subcontractor, gramee, ^«SSSi?^,. fenae activity or other organization fcoiporale author) issuing the report, 2a. REPORT SECUHTY CLASSIFICATION: Enter the ovef all aecurity classiflcatton of the report. Indicate whether "Restricted Data" la Included. Marking la to be in accordance with appropriate aecurity regulatlona. 26. GROUP: Automatic downgrading la specified In DoD Directive and Armed Forces Industrial Manual. Enter the group number. Also, when applicable ahow that optional markinga have been raed for Group 3 and Group 4 aa author- Ked. 3, REPORT TITLE: Enter the complete report title In all capital letters. Titles In all cases should be unclassified. ÄsÄl title cannot be selected without «UwUh* tlon, show title dessiflcatlon In all capitals In parenthesis immediately following the title. I, DESCRIPTIVE NOTES: If appropriate, enter the type of report, e.g.. interim, progress, summary, annual, or final. Give the Inclusive dstes when a specific reporting period Is covered. 5. AUTHOR(S): Enter the named) of thok«) I»*" O" or in the report. Ente, last name, first nsme, ^* ne J" 1 "? 1 - If ndlitsry, show rsnk and branch of service. The nsme of thrprincipsl -uthor is an absolute minimum requirement 6. REPORT DATE: Enter the date of the report as day, montryear! or month, year. If «ore than one date appears on the report, use date of publication. 7«. TOTAL NUMBER OF PAGES: The total page count should follow normal pagination procedures, I.e., enter the number of pages containing Information, 7b. rumber OF REFERENCES: Enter the total number of references cited In the report. 8a. CONTRACT OR GRANT NUMBER: " «PP'»"««'~ t " "e sppllcable number of the conteact or grant under which the report was written. 86, 8c, «. 8d. PROJECT NUMBER: Enter the»'op'»? 1» mi itary department identification, such a. project number, suhproi«ct number, system numbers, task number, etc. 9.. ORIGINATOR'S REPORT WMBER(S): Ent«the offl. cisl report number by which the document wul be Identified «d An ^STthe originating activity. Thla number muat be unique to this report. bb. OTHER REPORT NUMBER(5): "' 'V^JlSiMtor assigned any other report numbers foilher 6y «he ottglmtor or 6y»ha sponsor), also enter this numbers). 10. AVAILABILITY/LIMITATION NOTICES: Enter any limitations on further dissemination of the report, other than those (4) (5) "U. 8. military agencies may obtain copies of this report directly from DDC Other qualified uaers ahall request through "All distribution of this report Is controlled. Qualified DDC users shall request through If the report has been furnished tc the Office of Technlcsl Services, Department of Commerce, for sale to the public, Indlcate this fact and enter the price, If knowiw 11, SUPPLEMENTARY NOTES: Use for additional explanatory notes. IZ SPONSORING MILITARY ACTIVITY: Enter the name of the departmental project office or laboratory sponsoring fpay Ing lor) the research and development. Include addreas. 13. ABSTRACT: Enter an abstract giving a brief and factual summary of the document Indicative of the report, even though it may alao appear elaewhere In the body of the technical report. If additional apace la required, a continuation sheet shall be attached. It la highly desirable that the abstract of classified reports be unclaaaifted. Each paragraph of the aba tract ahall «nd with an Indication of the mllltaiy aecurity classlflcbtion of the Inforraatlon In the paragraph, represented as <TS). (S), (C). or (V). There Is no limitation en the length of the abstract. However, the suggested length Is from 150 to 235 words. 14 KEY WORDS: Key words art technically meaningful terms or abort phrases that characterise a report and may be used as index entries for cataloging the report. Key»orfs must be selected so that no aecurity daaalflcatlon Is required. «fiers, such ss equipment model designation, trade name, military project code name, geographic location, may be used as key words but will be followed by sn indication of technical context. The assignment of links, rules, and weight» Is optional GPO»«6-551 TInclaaaified Security Classification